This invention relates to a felt construction for use in a papermaking machine, and more particularly to a felt construction which functions to minimize rewetting of the paper sheet upon exit of the sheet from the press nip of the papermaking machine.
Rewetting of a paper sheet upon exit of the sheet from the press nip of the papermaking machine is a recognized problem in the papermaking industry. Various patents address this problem, including Liu et al U.S. Pat. No. 4,199,401; Eklund et al U.S. Pat. No. 5,182,164; Ashworth U.S. Pat. No. 4,162,190; Nyberg U.S. Pat. No. 4,988,409; Cronin U.S. Pat. No. 3,556,940; Wicker U.S. Pat. No. 3,214,331; and Wicker et al U.S. Pat. No. 3,214,327.
It is an object of the present invention to provide an improved papermaking felt capable of efficiently and effectively removing water from the paper web at the press nip and preventing backflow of water through the felt upon release of the web from the press nip. It is another object of the invention to provide such a felt which is relatively simple in construction yet which performs in a highly satisfactory manner to remove water from the web and prevent rewetting.
In accordance with one aspect of the invention, a felt for use in dewatering fibrous material, such as a paper web in a papermaking machine, consists of a base fabric, a batt layer and a porous flow control layer formed of a hydrophobic material interposed between the base fabric and the batt layer. The base fabric, the batt layer and the flow control layer are joined together, such as by needling, to form a felt. When the felt is installed in the press section of the papermaking machine for dewatering the paper web, the batt layer receives water from the web, and such water is then forced through the pores of the hydrophobic flow control layer under pressure from the press nip of the papermaking machine. When the web exits the press nip and pressure on the felt and the web is relieved, the flow control layer functions to prevent backflow of water to the batt layer so as to prevent rewetting of the web. The flow control layer is preferably a sheet of synthetic spunbonded material, such as nylon, which is treated with a hydrophobic chemical composition, such as a cationic flourochemical to render the layer hydrophobic. If desired, a second batt layer may be disposed against the surface of the base fabric opposite the flow control layer and secured to the base fabric via a needling operation.
The invention further contemplates a method of making a papermaking felt. The method involves positioning a sheet of hydrophobic material between a base fabric and a batt material, and joining the base fabric, the batt material and the hydrophobic material together, such as by needling, to construct a papermaking felt, As summarized above, the sheet of hydrophobic material is preferably in the form of a sheet of spunbonded synthetic material, such as nylon, treated with a hydrophobic chemical composition.
Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.